Problem: If $x \bigtriangleup y = 2x^{2}+y^{2}$ and $x \veebar y = x(y-7)$, find $(1 \bigtriangleup -1) \veebar -2$.
Explanation: First, find $1 \bigtriangleup -1$ $ 1 \bigtriangleup -1 = 2(1^{2})+(-1)^{2}$ $ \hphantom{1 \bigtriangleup -1} = 3$ Now, find $3 \veebar -2$ $ 3 \veebar -2 = 3(-2-7)$ $ \hphantom{3 \veebar -2} = -27$.